The present invention relates to infrared (IR) microscopy and thermal analysis generally and, more particularly, to a staring infrared microscope (IRM) for operating in the medium and long wave IR subregions. The present invention also relates to a scanning IRM for operation in the long wave IR subregion.
IRMs include optics for focusing IR radiation on IR sensitive detectors for producing an electric signal having an intensity proportional to the IR signal intensity impinging thereon. For staring and scanning IRMs, IR detectors are typically prepared from InSb and Cd.Hg.Te (CMT) semiconductor material, respectively. Other suitable materials are described in a chart entitled "Transmission regions of optical materials" in The Infrared Handbook, pg. 7-17 prepared by The Infrared Information and Analysis (IRIA) Center, Environmental Research Institute of Michigan.
The performance rating of an IRM is typically described in terms of two parameters. First, its spatial resolution defined as the smallest distinguishable dimension of an object. Second, its thermal sensitivity defined as the smallest distinguishable temperature difference between adjacent portions of an object. For convenience, thermal sensitivity performance is often given in terms of its noise equivalent temperature (NET) which is the temperature difference equivalent to the RMS noise signal.
Various infrared microscopes and their use in a range of infrared microscopy and thermal analysis applications, for example, non-destructive failure analysis of integrated circuits, microprocessors etc., and bio-engineering applications, such as identification of bacteria are now described.
Shell et al., in "Applications of Infrared Microscopy for Bond Pad Damage Detection", in the 1991 IEEE/IRPS Journal, pp. 152-159, which describe an IRM operating in the wavelength region of about 0.8 to 1.8 microns for the non-destructive failure analysis of plastic encapsulated devices.
Yasuda et al., in "Direct Measurement of Localized Joule Heating in Silicon Devices by Means of Newly Developed High Resolution IR Microscopy", in the 1991 IEEE/IRPS Journal pp. 245-249, which is described an IRM which combines a ZnS objective lens and a Hg.Cd.Te IR detector having a maximum sensitivity around the 8 to 12 .mu.m wavelength to achieve a practical spatial resolution of 10 .mu.m and temperature resolution of 0.24K.degree..
PCT Patent Application PCT/DE90/00081 to Bruker Analytische Messtechnik GMBH entitled "Process and Device for Rapid Detection of Micro-organisms in Samples", which is incorporated by reference as if fully set forth herein, describes a process and a device whereby IR radiation is passed through a culture for obtaining the number of micro-organisms in a sample and for identifying specimens using IR spectra information.
Several shortcomings of the above described IRMS include low thermal sensitivity particularly at high magnifications and the use of optics and other items, for example cold shields, which have not been engineered to achieve optimum performance in medium and long wave IR applications.
There is thus a widely recognized need for, and it would be highly desirable to have, a staring IR microscope having a magnification capability of up to 40X or thereabouts while rendering a thermal sensitivity of 0.02K.degree. at a spatial resolution of 3 .mu.m. Such a staring IRM can be used for the above mentioned applications and other bio-engineering applications such as differentiation between microbiological specimens, the determination of the morphology of tissues, and comparison of growth rate between different cultures for creating a database of metabolic growth rates of bugs, tissues, micro-organisms and the like for comparative and correlation purposes.
The staring IRM is capable of providing up to 40X magnification or thereabouts without loss of thermal sensitivity by virtue of novel control apparatus which adapts the integration time T of the IR detector as a function of the magnification M of the IRM's optics according to, but not limited to, the following function: EQU T=k(M+1).sup.2 where k is a constant
Still further, it would be highly advantageous to have a combined visible and staring IRM for displaying ongoing temperature changes during thermal rate processes to facilitate recognition and evaluation of the object under examination by the user.